Enhanced NLO response and switching self-focussing in benzodiazepine derivative with -NO₂ and -Br substitution

Optoelectronic and the cubic nonlinear optical properties of 4-(4-Bromophenyl)-2-(4-nitrophenyl)-2, 3-dihydro-1H-1, 5-benzodiazepine have been studied. Z-scan technique was used for the third-order nonlinear optical measurements namely, nonlinear absorption, nonlinear refraction, and optical power limiting behaviour employing an Nd: YAG laser of 532 nm wavelength having 5 ns Gaussian pulses. B3LYP/6-311 ++ G (d, p) level of theory was employed for structural optimization, vibrational wavenumber, frontier molecular orbitals, natural bond orbital and population analysis. The MOLVIB programme was used to perform unambiguous vibrational assignments based on potential energy distribution values acquired from normal coordinate analysis. B3LYP and CAM-B3LYP hybrid functions have been employed at the DFT level to calculate the theoretical second-order hyperpolarizability. The substitution of -NO₂ and -Br in this benzodiazepine compound enhances the second-order hyperpolarizability (γ) to the order of 10^-34 esu and, switching of self-defocussing to self-focussing phenomenon. The HOMO-LUMO and optical band gap analysis illustrates that polarizing nature of the molecule vary with substituents. The obtained results indicate that this compound has potential applications in optoelectronics and photonics.